1. Field of the Invention
The present invention relates to an illumination unit and a liquid crystal display device including the illumination unit.
2. Description of the Related Art
Liquid crystal display devices have been used in various fields as display devices of OA equipment, such as personal computers, and TV receivers, taking advantage of their features of light weight, small thickness and low power consumption. In recent years, the liquid crystal display devices have also been used as display devices of portable terminal devices such as mobile phones, car navigation devices, and game machines.
As such liquid crystal display devices, a reflective module which displays an image by selectively reflecting ambient light, a transmissive module which displays an image by selectively transmitting backlight, and a transflective module having both functions of the reflective module and transmissive module, have been developed.
The transmissive liquid crystal display device is configured to include a transmissive liquid crystal display panel and an illumination unit (i.e. a backlight) which is disposed on the back side of the liquid crystal display panel. In recent years, an illumination unit in which a light-emitting diode (LED) is applied as a light source has been put to practical use as the above-described illumination unit which is mounted in the liquid crystal display device.
Patent document 1 (Jpn. Pat. Appln. KOKAI Publication No. 2003-76287), for instance, discloses a backlight device in which a plurality of semiconductor light-emitting elements (LEDs, or light-emitting diodes), each having a light emission surface that is substantially perpendicular to a mounting surface thereof, are mounted in a string fashion on one surface of a film substrate. The backlight device is housed in a metal frame in the state in which the one surface of the film substrate is attached to a surface of a light guide such that the light emission surfaces of the semiconductor light-emitting elements are put in close contact with a light incidence surface of the light guide.
In particular, according to patent document 1, in order to escape heat occurring in the semiconductor light-emitting elements to the metal frame, a metal thin film for heat radiation is provided on almost the entirety of the other surface of the film substrate, on which the semiconductor light-emitting elements are not mounted, and the metal thin film is pressed by the metal frame. Further, according to patent document 1, so-called side-view-type LEDs are used as semiconductor light emission elements, and the film substrate is firmly adhered to a wide area of the light guide.
The light-emitting diode has such characteristics that the light-emitting diode produces heat in operation, and that the light-emitting diode tends to easily deteriorate in a high-temperature environment. Thus, in order to increase the lifetime of the light-emitting diode, there has been a demand for the enhancement of heat radiation efficiency, and for the driving in a low-temperature environment.
Moreover, there has been a demand for easy replacement of the light-emitting diode in case where the light-emitting diode has deteriorated. In the structure wherein the film substrate, on which the LEDs are mounted, is attached to the light guide, as disclosed in patent document 1, a work is needed to disassemble the backlight device and peel the film substrate from the light guide. The replacement work becomes more time-consuming as the film substrate is more firmly attached to the light guide.